Episode 372 is all about Chindesaurus, Basal saurischian that lived in the Late Triassic in what is now Arizona.
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In this episode, we discuss:
News:
- A new ankylosaur, Stegouros elengassen, was described with amazing spikey tail weaponry from Magallanes, Chile source
- The new sauropod, Rhomaleopakhus turpanensis, was named from the Xinjiang Uygur Autonomous Region, China source
- Chief Shikellamy Elementary School in Sunbury, Pennsylvania have a new 6 ft Diplodocus femur on display source
The dinosaur of the day: Chindesaurus
- Basal saurischian that lived in the Late Triassic in what is now Arizona, US (maybe also New Mexico and Texas)
- Looks like a small theropod, walking on two legs and had a long tail
- Type and only species is Chindesaurus bryansmalli
- Found a partial skeleton in the Petrified Forest National Park in 1984 (was airlifted out in 1985)
- In the 1920s, Charles Camp from the University of California at Berkeley collected fossils and took photos of the Petrified Forest. In the 1980s, Robert Long from Berkeley found Camp’s sites. Bryan Small, who was on the team collecting fossils, found the ankle bone of Chindesaurus
- At the time Chindesaurus was found, it was thought to be the oldest dinosaur ever found
- Holotype has a nickname, “Gertie”, after Gertie the Dinosaur
- Also known as the “Chinde Point dinosaur”, because of where the specimen was found
- Described in 1995 by R.A. Long and P.A. Murry
- Genus name means “ghost lizard” or “lizard from Chinde Point”
- Genus name comes from the Navajo word chindi, which means “ghost” or “evil spirit”
- Species name is honor of Bryan Small, who found the holotype
- Holotype includes vertebrae, limb bones, and hip fragments
- Holotype was prepared at the University of California Museum of Paleontology in Berkeley, California
- Fragmentary skeletons have been found in Arizona, New Mexico, and Texas, but not all of these may belong to Chindesaurus
- Referred specimens are incomplete and include vertebrae and femur fragments, although one complete femur was found in 2006 in Ghost Ranch, New Mexico
- However, some of these referred specimens may not be Chindesaurus, because they don’t have features unique to Chindesaurus
- In 2019, Adam Marsh and others said only the holotype should be considered to be Chindesaurus
- A partial lilium found in Texas (Tecovas Formation) was thought to be Chindesaurus and then in 1998, Hunt and others named it as a new taxon, Caseosaurus crosbyensis
- However, in 2004 Langer said these two were the same species, and Nesbitt and others supported the idea in 2007, saying what made Caseosaurus and Chindesaurus different was just variation in size (but they didn’t formally synonmize the two, because the ilium of Chindesaurus is too fragmentary)
- In 2018 Baron and Williams redescribed Caseosaurus and found it to be valid
- Holotype of Chindesaurus may not be an adult, based on an unfused ankle
- Long and Murry estimated Chindesaurus to be 9.9 to 13.1 ft (3 to 4 m), and to have a stout body, long legs, and a long neck
- In 2012, Benson and Brusatte estimated Chindesaurus to be 6.6 to 7.5 ft (2 to 2.3 m) long
- Also in 2012, Holtz estimated Chindesaurus to be about 6.6 ft (2 m) long and weigh about 50 to 100 lb (23 to 45 kg), or about the same as a wolf
- No skull has been found
- Had large tail vertebrae at the base that got longer towards the tip of the tail
- Had long, low cervical vertebrae, so neck was probably light and slender
- Had a large, crescent-shaped femur
- Lots of debate over what type of dinosaur Chindesaurus was. At times thought to be a basal sauropodomorph, then later thought to be a herrerasaurid
- In 2007, Nesbitt and others and Irmis and others suggested Chindesaurus was a basal saurischian
- A phylogenetic analysis found Chindesaurus to be a sister taxon to Tawa hallae (previously Chindesaurus was thought to be a herrerasaurid and Tawa a theropod). Chindesaurus and Tawa were placed within basal Saurischia, before sauropodomorphs and theropods split off
- In 2019 Adam Marsh and others redescribed Chindesaurus and found Chindesaurus and Tawa to be “a potentially diverse group of early theropods prior to the end-Triassic mass extinction”
- In 2019, Morgan Schaller and others, researchers from the Rensselaer Polytechnic Institute and University of Texas Austin, found that oxygen levels rapidly increased over a 3 million year period around the time Chindesaurus lived
- They analyzed small amounts of gas from rocks from the Colorado Plateau and the Newark Basin (about 621 mi or 1,000 km away from each other on Pangea and near the equator), which were around 215 million years old
- Found that oxygen levels went from 15% to 19% and there was a drop in carbon dioxide levels (today we have 21% oxygen)
- Probably was a global change in oxygen levels
- Around the oxygen peak is when some of the first dinosaurs appeared in the tropics of what is now North America, like Chindesaurus (though dinosaurs were in what is now South America earlier, about 232 million years ago). Sauropods came soon after
- Higher oxygen levels may have helped animals grow larger
- At the very least, the environmental changes were good for evolutionary diversification, though there may have been other factors that helped
- Chindesaurus lived on an ancient floodplain
- Other animals that lived around the same time and place include archosaurs, pseudosuchians, tetrapods, phytosaurus, Coelophysis, lungfish, and clams
- A short documentary, about 30 minutes, was made about Chindesaurus in 1988, called “A Whopping Small Dinosaur.” About the expedition and assembly of Chindesaurus
Fun Fact: Stegouros is the only named dinosaur from Magallanes, Chile and the southernmost of any dinosaur (excluding Antarctica).
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